DALLAS, Jan 13 (Reuters) - The intoxication manslaughter trial of former Dallas Cowboys player Josh Brent started on Monday with prosecutors saying the defensive tackle was operating with reckless abandon when he crashed his car in 2012, killing his teammate, Jerry Brown Jr.

Brent's lawyers said their client had made a terrible mistake but was not intoxicated when he got behind the wheel.

Brent, 25, is accused of being drunk when the Mercedes he was driving at a high speed flipped over and then caught fire on a state highway on Dec. 8, 2012.

When police arrived, they found Brent dragging Brown, 25, out of the burning car, which was resting on its roof in the middle of the road.

Brown, who had been riding in the passenger seat, was pronounced dead at a Dallas hospital a short time later.

"He was so intoxicated, he did not appreciate the danger of traveling at that high rate of speed when he exited (the highway)," Dallas County prosecutor Heath Harris told the jury.

A police affidavit stated that an officer had smelled alcohol on Brent's breath and found an unopened bottle of cognac inside the vehicle. Brent initially refused a blood sobriety test but was forced to comply after Brown's death.

Brent's blood alcohol level was 0.189, according to police documents. The legal limit in Texas is 0.08.

Defense lawyer George Milner told the court that the amount of liquor Brent drank before getting behind the wheel was not enough to make him drunk because of his large stature. Brent's playing weight was 320 pounds (145 kg).

"Josh Brent is as big as a house," Milner said. "He's guilty of being stupid behind the wheel of a car. He is guilty of driving too fast. We're not going to dispute that."

The trial at a courtroom in Dallas County is expected to take as long as two weeks.

If convicted, Brent faces two to 20 years in prison and a fine of up to $10,000.

Brent was put on leave from the Cowboys after the accident and retired in July, saying he had other priorities in his life more important than football.

"I am devastated and filled with grief," Brent said in a statement shortly after the crash. "I will live with this horrific and tragic loss every day for the rest of my life." (Reporting by Lisa Maria Garza; Writing by Jon Herskovitz; Editing by Scott Malone and Lisa Von Ahn)